Simple definition
PIM Dense Mode initially floods multicast traffic and then prunes branches with no interested receivers.
Purpose and use
PIM-DM, Protocol Independent Multicast Dense Mode, distributes streams on the initial assumption that receivers may exist on many branches.
How does it work?
Traffic is initially flooded over eligible paths, then uninterested branches are pruned. RPF checks use available routing information.
Example and verification
For unexpected multicast traffic, examine prune state and outgoing interfaces rather than only endpoint membership.
Points to watch
Initial flooding can consume bandwidth where few receivers actually want the stream.
In short
Dense mode uses a different distribution assumption from sparse mode; select the mode according to topology and actual requirements.